I. Field of the Invention
The present invention relates to the visual arts field and more particularly to autostereoscopic imaging apparatus and methods for producing two-dimensional images that, on display two-dimensionally, can be perceived three-dimensionally without the use of special viewing aids.
II. Prior Art
The production of two-dimensional images that can be displayed to provide a three-dimensional illusion has been a long standing goal in the visual arts field. Methods and apparatus for producing such three-dimensional illusions have to some extent paralleled the increased understanding of the physiology of human depth perception, as well as developments in image manipulation through analog/digital signal processing and computer imaging software.
Binocular (stereo) vision requires two eyes that look in the same direction with overlapping visual fields. Each eye views a scene from a slightly different parallax angle, and focuses the scene image onto the retina, a concave surface at the back of the eye that is lined with nerve cells or neurons. The two-dimensional retinal images are transmitted along the optic nerves to the brain's visual cortex, where they are combined in a process known as stereopsis to form a three-dimensional model of the scene. What stereopsis is and how it is performed are still matters of some debate.
Perception of three-dimensional space depends on various kinds of information in the scene being viewed, e.g., monocular cues such as relative size, linear perspective, interposition, and light and shadow; binocular cues such as retinal disparity (parallax information), accommodation, and convergence; and learned cues (familiarity with objects in the scene).
Parallax information does not have to be presented to the brain simultaneously. It is known that left and right eye depth information can be presented alternately to the left and right eyes, resulting in depth perception, as long as the time interval does not exceed 100 msec. The brain can extract parallax information from a three-dimensional scene even when the right and left eyes are alternately covered and uncovered for periods of up to 100 msec each. The brain can also accept and process parallax information presented concurrently to both eyes if sequenced properly. The ideal view cycle sequencing rate is between 3-6 Hz.
True three-dimensional image displays can be divided into two main categories, stereoscopic (also known as binocular) and autostereoscopic. Stereoscopic techniques (including stereoscopes, polarization, anaglyphic, Pulfrich, and shuttering technologies) require the viewer to wear special viewing glasses. Autostereoscopic techniques (such as holography, lenticular screens, parallax barriers, and alternating pairs, and parallax scans) can produce images with a true three-dimensional illusion without the use of special glasses.
Prior art autostereoscopic television and motion picture systems have utilized the approach of alternately displaying views of a scene recorded by two cameras from different points of view. U.S. Pat. No. 4,006,291 to Imsand; U.S. Patent No. 4,303,316 to McElveen; U.S. Pat. No. 4,429,328 to Jones et al.; and U.S. Pat. No. 4,815,819 to Mayhew et al. all utilized two cameras to record horizontally, vertically, or a combination of horizontally and vertically displaced views of a scene. While this autostereoscopic approach produces images which provide a three-dimensional illusion when displayed, it does not have a stereoscopic appearance like that of a 3-D movie. Another drawback is image instability resulting from the alternation of the points of view.
Attempts to control autostereoscopic image stability have resulted in variations of the prior art methods mentioned above. U.S. Pat. No. 4,567,513 to Imsand and U.S. Pat. No. 4,528,587 to Jones disclose methods to control image instability through video signal processing, resulting in mixed images which are not of a commercially exceptional quality.
Another approach to controlling autostereoscopic image stability is through single lens parallax scanning methods, as exemplified by U.S. Pat. No. 5,014,126 to Pritchard and Mayhew, copending U.S. patent application Ser. No. 08/115,101, filed Sep. 2, 1993 by Fernekes et al., and copending U.S. patent application Ser. No. 08/148,916, filed Nov. 5, 1993 by Bacs, Jr. While these methods produce autostereoscopic imaging of exceptional quality and stability, they do not produce an image having a stereoscopic appearance like a traditional 3-D movie which requires special viewing glasses.